one's BFFL, or Best Friend For Life. it is supposed to be the opposite sex, whom one is JUST friends with, and wouldn't ever date. however many biffles become boyfriends, which really defeats the purpose. unlike best friends, you can only have ONE biffle.

Usually a great friend of the opposite sex who you can trust with your life. However, someone who is a biffle is not necessarily stuck in the "friend zone", as biffles often make the best couples. Often, a girl may instigate a biffle relationship as a way of flirting. It is customary to be protective and loyal to your Biffle.